FWD/FF Buggy

[Origineelreclamebord]

The last prototype had some kickup and some adjustability... I was adviced to minimize the kickup on the car. It added traction - I recall primarily forward traction, but I'd have to look back in the notes I made and things I wrote in this topic

This - and for the gearbox/donor car that I chose - the front of the car has 0 kickup. It can (probably) be adjusted with the RDRP Low Roll Center suspension hangers, but that's something to test when I know more about what's on the car right now.

Anti-squat is a whole different matter on this car. To begin with the rear end doesn't even use double wishbone suspension but trailing arms. I guess anti-squat here would be achieved by moving the hinging point of the rear arms up. I will try this out soon to see if this is indeed true At the front, the kickup forms anti-squat, and this may well be the reason that reducing kickup works to maintain grip on the front on acceleration (because when the weight shifts to the rear you don't pull it out of the front suspension as much.

Caster is quite minimal (standard DEX setting) - I can increase the caster, and it's worth trying out... but then it may be good to ask first who I could borrow a set from - it's so much cheaper I can always still buy them when they work.

[Burty248]

Sounds like you have a lot of testing to do. I guess it is still a prototype. I wish i had the resorces to build my own parts for my car but i think it is on hold for now.

Sorry if ive been asking a lot of questions but this car is so intresting its hard not to.

[Origineelreclamebord]

Hehe thanks Ask away, the more people are asking questions on this car, the higher the chances are of finding useful improvements on the car

I've just driven the car some more on the same tarmac patch. I've used some harder rear springs and put a little toe-out on the front. The springs didn't make a big difference, the toe-out did make a difference worth mentioning. It added steering into corners, and in combination with the harder springs the rear end can finally be persuaded to let the front end do what it's supposed to.

That said, the adjustments I have made are all small tweaks and I'm starting to notice I want bigger changes than what those can give me. Much like the first onroad test I can't be sure how accurate the test is for astro: not so much because of grip levels, but because of how the car reacts to bumps. The car has near zero rear droop at the moment and it's still hanging in there onroad, but I think that would make it rather unpredictable offroad... My prediction is that I need to increase rear damping/pack, use harder springs and increase rear droop to make it work on astro We'll find out in a few weeks I guess - in the meantime these onroad tests do give me a better feel of what the small changes may do to the car.

[Origineelreclamebord]

Small update - but potentially crucial. It really bugged me that the motor's wiring lugs and sensor connection were unprotected from impacts and crashes - one bad hit against a fence, wall or another trackside object in the wrong spot and the motor is done for.

Now I could just have made an add-on piece to solve this, but I thought I'd try and make use of the flexibility that the printed nylon offers to (hopefully) make a slightly more flexible bumper - but as it's mounted on both top and bottom still miles stiffer than the original small bumper I had printed

The side plate should offer some protection in a crash - yes, forces may still be transferred and the plate might sacrifice it's life in a really bad situation, but then at least my motor still works It's not the most elegant solution, but for now it'll have to do - it's too much work to make add-ons look nice that might not work at all

[Origineelreclamebord]

So last weekend I extensively drove the car on astro... both in wet and in dry conditions!

The result? In the end, very nice! In the contrary to earlier tests on tarmac and even an (extremely low bite) astroturf tennis field, the car lacked rear stability/bite on the rear.

It turned out the rear end needed minispikes on the rear instead of cut staggers, more droop, and (shame on me) better filled shocks

I got more and more people saying the wing needed to go further back, and up. After doing so, it seemed like the wing stabilized the rear more - not just on the ground, also in the air it seemed a little more consistent.

After this, I experimented with the gearbox. First off, I switched from an 83 to a 78T spur - it's almost hugging the casing now. If it was a switch from the kit (87T) spur the differences would've been more noticable... but for me, it felt as if the car turned a little quicker. I'm sure it helps on other things too, like going over bumpy sections and jumping/flying, but to be honest by that time I was getting pretty sleepy.

Then as a final thing, I wanted to test the 4-gear gearbox. The test of 3-gear vs. 4-gear had a night's sleep between them, so I will be re-doing this test... But I would say so far that the difference isn't like night and day, but it does seem to be more stable on the brakes/when decelerating, and it seemed more eager to get away on-power.

What struck me was how easy it was to jump despite the windy conditions. I think it´s got something to do with the new piston setup I was running, in combination with the small spur, high wing etc... but whatever the case, it was jumping perfectly flat very consistently, even in pretty windy conditions it seemed to fair pretty well with it.

I also asked X-Factory test driver Bruno Heremans (Elvo) to drive the car in the dry. He almost immediately asked me to increase the rear toe-in. After that he tested it some more. He too seemed surprised by the jumping characteristics.

After the test I received his verdict on the car, with a list of very nice ideas where the car could be improved. The basics of the car are good, the suspension geometry decent and the weight balance is very nice, but there are some points that need attention. The way it seems now these changes can all be implemented in an evolution of this car, not a redesign from scratch like I did between the previous and current prototype

So the performance is very good so far. Also, the car's durability seems good so far: No carbon or 3D printed parts have broken yet after two proper test days/events. I have encountered small damage/issues with Durango parts and that lexan bumper from the first test, but all of that still is pretty minor stuff... and I'm not driving it as if it's delicate! Then lastly, tire wear is higher on the front than a regular 2WD on the rear, but it's not shocking.

[diago999]

Hi Origineelreclamebord,
I'd just like to say I have thoroughly enjoyed reading about your design project/prototype here, and I look forward to each comment you write so we can see how you and the car are getting on,

being quite new to RC I wish I could offer some advice but as I don't know much, so I'll steer clear of that!

Well done

[Origineelreclamebord]

Thanks I´m glad you like the thread!

I´ve gotten great ideas from people who are relatively unknown to RC racing just because they have a fresh view and rich imagination to the possibilities.... So don´t be afraid to share your ideas or ask questions... !

By the way, a nice update for everyone who's going to the Kampenhout GP: This car will be raced in the 2WD class on Saturday! It's the most practical way to gather accurate data on the car's current pace, durability and how to behave with other cars around. I might put in a timed heat with the TRF (for which I have suitable setups already) as a base time to compare with... but the FF will be my main car for the race!

This decision was taken after today's training at Kampenhout. It goes well and the car has a distinct advantage over the two cobblestone hairpins in the track because many RWDs struggle for a combination of stable and quick acceleration there.

I am currently dealing with some grip roll issues: The car is slightly narrower than most 2WDs and I didn't have firmer pistons with me or a front stabilizer. I'm doing my best to make these parts ready for the weekend, but I have found a few ways to reduce the grip roll without them. This includes a considerable reduction of the droop on all corners... not an ideal solution, but the side-effects are relatively small on the fast, flowing and flat track (low jumps) and by the end of today's training/testing session it felt really fast, competitive and consistent!

[Phil Channon]

You could also try putting a layer of superglue on the tyre sidewalls. This should reduce some sidebite.

[Origineelreclamebord]

Originally Posted by Phil Channon

You could also try putting a layer of superglue on the tyre sidewalls. This should reduce some sidebite.

Certainly worth a shot on some older tires I know there are patches with new astroturf on Kampenhout and overall grip is quite high... but a RWD or 4WD doesn't need it. So there must be a way around too much butchering of the tires. That, or it turns out over time that an FWD is an exception to this rule...

[Burty248]

Its common to remove some tread on the front tyres of 4WD cars so possibly your FWD would benefit from it too.

[madmax]

It was brilliant to see the car running and even have a go, the pace of the car is very good and seemed to have more grip than some rwd cars on sat, it even held its own with the 4wd on sun.

Lee

[Origineelreclamebord]

Thanks Lee It was a fun weekend and I really appreciate the help on the setup of the car!

The car went really well at the Kampenhout weekend and the training. I've tried the following things:

- Gear Diff: Awesome in the dry, not impressive in the wet. In the dry it makes the acceleration very direct and aggressive, however in the wet the diff seems to be too aggressive to put the power down efficiently.
- Front stabilizer: Worked well in the dry to reduce grip roll, in the wet it caused understeer and the car was then better off without it.
- Thicker oil in the rear: The car's rear end is getting more stable on jumps, but the car's F/R stability is still not 100% there.
- Bigger rear wing (LMR wing, full gurney): Any imbalance on the rear at high speed was damped and corrected, it felt calmer with the bigger wing.
- Extra weight around the LiPo: It doesn't really change the weight balance, which is nice. In the dry the 140g of weight helped to reduce grip roll and made it more planted. In the wet I felt the car was better off with 100g weight less - mainly for reasons of acceleration, plus the weight wasn't necessary anymore to fight grip roll.
- Tires: Good tread was quicker, but not a huge difference in terms of acceleration. It was in terms of steering, which has both pros and cons. The pro being that it should be quicker, the con being that it is less confidence inspiring because it grip rolls easier.
- Roll balance: In the dry I was running 2mm spacers on the inside and none on the outside, it felt less agressive and more forgiving to grip roll. In the wet I used 2mm spacers on the outside and none on the inside to gain some agression on the front end. Madmax suggested to me to try long links by moving the outside ball stud to the top of the steering knuckle. It seemed to make the front end more stable and grippy, but in this case also made the rear end quite unstable in the cobblestone sections. Also, the adjuster rubbed the wheel slightly. It's an interesting thing to try out again soon when I've removed some material off the top of the steering knuckle to make some clearance

I've also had some other people drive it: Tony Parr, Kevin Lee, Arjan v/d Graaf, Bruno Heremans (2nd time), Wesley van Helmond (winner of the 2WD class this year) and several other people. The response seems generally positive, but I've got a few reoccuring comments on the car:

- The car is unstable off-power. It can result in a lack of turn-in, the rear-end stepping out or the car making stoppies when braking.

I've already/apparently adapted my driving style where, if I brake or go off-power, I do this before a corner and go on-power on turn-in so the car is always on power when it's not going in a straight line. I think it's something the car inherits from the weight balance it needs to accelerate well, just like a rear-motor RWD makes wheelies to easily and has oversteer that is hard to correct. Of course though, I will do everything I can to minimize the unintended handling traits and maximize the intended ones

- The steering is really progressive near full lock, which makes it twitchy to drive at times.

This may come from several things. First of all, the steering rack's geometry makes the steering quite progressive. Secondly, I've been pointed out by Bruno Heremans that the steering rack has too much flex in it. And on top of that I found that the servo mounts are not yet stiff enough (the servo moves back and forth when the wheels encounter resistance against steering). If I manage to improve on these three points the steering should be much more predictable.

The advice really helps, and so does that I've got some 140 pictures and a 1:30 minute video of the car in action! There is lots of stuff to work on and go through, but that only means there will a positive curve in the car's performance

Note: I'll upload the album soon with the best pictures in there.

[tramp]

Looking forward to the pictures and videos!

[Origineelreclamebord]

Here you go: > LINK <

Besides regular pictures there are also a few strings of continuous shooting I put together into one picture Look closely and you'll notice some changes to the car throughout the day and compared to the standard spec: wing extension (not elegant but works), front stabilizer (tucked away between all the stuff at the front end), switch to a bigger wing...

I'll make some body-off pictures of the chassis as well soon - then you can see what the chassis layout is like with electronics in - It's tight but considering the electronics I have are pretty huge it's acceptable.

[elvo]

http://www.youtube.com/watch?v=MGK3k...e_gdata_player

[Origineelreclamebord]

Thanks elvo! Because there are now several videos of the car on Youtube, I decided to put them together in a playlist. Much easier! And all videos that will be posted I'll add to the playlist. Here are the links:

Complete playlist

My latest footage of the car

This latest footage is from Tony Parr (2WD B-finalist at the GP) making his first laps with the car. It was a bit busy and the 4WD drivers didn't seem to know how to get around the car, so it seems everyone made the call to try and go through the car

Anyway, one of the things Tony mentioned is that the car's steering is too progressive - and it's probably something with the geometry of the steering rack combined with the flex in the steering rack: It makes the car steer quite suddenly and at times, hook. It's visible in the video that the car is suffering from it. I seem to have grown used to it and adapted my driving style to minimize it, so it's really useful to get the input from drivers like Tony!

[Origineelreclamebord]

I've had a bit of a break with the car because the development of it has consumed the majority of the events I went to the last few months. Besides that, I have gathered so much data that I have to process that first and decide what developments I can make - there's not much point in driving a prototype without testing new things after all

I may be able to get slightly more out of the car as is, but for the bigger steps in performance, updates to the construction are required. The steering flex was mentioned before in the topic, and it's been appointed as the first thing to change on the car. It's preferable to change as little as possible to the rest of the car to test this, both from a cost perspective as for the purity of the testing result. So far I've been struggling with a really good solution, but today I had a bit of a brainwave I can do this with the current steering rack, only a little dremeling is needed and a small steel plate!

Go back to page 9, and you may notice the chassis layout there has the link between steering rack and servo on the outside of the chassis. I changed this to allow a lower profile body, but always kept the compatability on the chassis to revert to the edge of the chassis... and this is exactly what I'll be doing! By doing so, the steering rack plate can me reversed (it doesn't need to clear the ball joint of the servo arm anymore) - this means I can lower it by 4-5mm by Dremeling material off the top of the steering arm. The difference is shown below (Left = Old, Right = New):



The lower steering rack plate reduces the distance between that plate and the ball joints of the tie rods - reducing the flex in that particular area by 30-40%!

The other part of the mod will be a small steel plate that connects the servo to the top chassis plate in the center, whereas it was only mounted to the bottom chassis plate before - this will prevent the excessive flex currently present around the servo when under load.

I hope to have the steering mods ready for my next race this weekend, which is on grass. It'll be the first time for me with an FWD buggy on grass, as well as the good test opportunity with high grip levels!

[Origineelreclamebord]

This video might say 'something' about how today went I guess (thanks Elvo ):

http://www.youtube.com/watch?v=bB9_PiL5MGM

All irregular things the car does in that video (like the weird crash at the jump) is when my clumsy driving button is switched on for a few seconds

This video was taken during a break between qualification and finals - the results were BQ and a very dominant pace in the finals (the second and third heat I had a 20 second lead - in the second heat a driveshaft problem caused retirement, the third heat saw me reaching the finish with that lead)... This was enough to take first place in the B-finals! I'm really happy with the result, considering the 29 driver field for 2WD and seeing who ended above me, a RWD wouldn't have gained me many spots in the field - if at all.

So the day went great - with some minor setup changes to the rear end (stiffer damping+springs and more droop) and the steering mod (which made me feel more 'in control' of the car - it just seemed more consistent and more accurate to the input I gave it).

[johnnygibbon]

this car just gets better
looked very smmoth and controlled on the grass and in the air
awsome

[skyaflake]

Car looked great! A great piece of craftsmanship. I was in the same final as you but you were just too fast (going back to stick doesn't help either ). You had so much pace and the car jumped pretty good as far as I could see.

Hope to see more of it soon. Keep it going.

Is it (the drawing and manufacturing) your profession or just as a hobby?